[ECOS] powerpc-eabi-gdb backtrace problem

[Jonathan Larmour]

Nick Garnett wrote:
> Jonathan Larmour <jifl@eCosCentric.com> writes:
> 
> 
>>Well if there's a problem it's with the HAL. HAL_THREAD_INIT_CONTEXT
>>is called _after_ all the padding is added, and it's that which should
>>add any relevant space. For the powerpc, it already leaves
>>CYGARC_PPC_STACK_FRAME_SIZE which is a whole 56 bytes (which looking
>>at the eABI I saw, looks like overkill).
> 
> 
> If I recall correctly the EABI needs 7 words -- 4 argument save
> locations, return link, frame pointer, TOC pointer. I chose to allow
> twice that just to give us a safety buffer at the top of the stack.

That plus some of them in the ABI I saw says are optional: 
http://www-3.ibm.com/chips/techlib/techlib.nsf/techdocs/852569B20050FF77852569970071B0D6/$file/eabi_app.pdf
Sorry about the long link.

>>However I also note that area
>>isn't initialized to anything. But then we'd see it without the stack
>>frame checking enabled either.
> 
> 
> In the absence of stack checking these locations will mostly be zero,
> so GDB terminates. I guess that at least the frame pointer and return
> link need to be zeroed.

Well the stack checking shouldn't reach that far in general - it only 
fills stuff round the edges of the stack. But let's see...

Christoph, can you try the attached patch with the stack checking 
re-enabled to see if it fixes the problem?

Well, actually it only fixes _a_ problem... the stub shouldn't fail like 
it did if it gets a bad address _anyway_. GDB's heuristics can fail for 
other reasons, e.g. aggressive optimisation.

Jifl
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